1. Field of the Invention
This invention relates to a color display apparatus for enabling color reproduction capable of dealing with all of supplied image signals in the display of image signals having reference white colors and/or image pickup characteristics associated with plural different color reproducing regions.
2. Description of the Related Art
In color television receivers in general, color reproduction is achieved by additive mixing of three prime colors. The color television receivers have color reproduction characteristics based on colorimetry or colorimetric parameters. By these color reproduction characteristics, appropriate color reproduction is achieved by the receiver over a wide range using parameters such as chromaticity points of reference white and three prime colors on the receiver side. To this end, various color reproduction methods have been proposed.
For indicating colors of an object or a light source by these various color reproducing methods, chromaticity points are indicated by points of intersection on an xy chromaticity diagram represented by CIE chromaticity coordinates (x, y). The colors of a light source or an object may be indicated by three prime colors on the receiver side, namely red (R), green (G) and blue (B), and reference white.
A standard C light source by CIE is adopted in, for example, the NTSC system, which is one of the current color television systems.
This standard C light source is among lights the relative spectral distribution of which is prescribed by CIE as a standard illumination employed for displaying colors of objects and is an ordinary daylight within a visible wavelength range having a correlative color temperature approximately equal to 6774K.
Recently, for obviating the above mentioned problems inherent in the television systems, a variety of new television systems have been investigated and proposed. One of such proposed systems is a high definition television system (HDTV system) proposed by Japan Broadcasting Corporation (NHK).
Among the specifications for HDTV system, studio standards are presently investigated by Comite Consultatif Internationale des Radio Communications (CCIR). A CCIR report 801 was proposed as recommendations in 1986. Under these recommendations, investigations were conducted by the Broadcasting Technology Association (BTA) and the Society of Motion Picture and Television Engineers of America (SMPTE) and the studio standards were completed except a part of digital standards. The studio standards were publicized as BTA-S001, while the studio standards by CCIR were publicized as recommendations by CCIR REC XA/11.
Meanwhile, the color reproduction regions are different for each of the television systems, such as the above mentioned current television systems or the HDTV system.
Consequently, if signals of the different color systems are entered to a television receiver, colors displayed on the screen are different from those intended to be displayed, i.e. color reproduction errors are produced.
Referring to FIG. 2, a color reproducing region 30 of the BTA standards and a color reproducing region 31 of the standards by CCIR REC XA/11, formulated with a view to global standard unification, are different from each other, despite the fact that they are both the standards for high definition television system, that is, these regions 30, 31 have different chromaticity points for the three prime colors. Therefore, even supposing that unification could be achieved in future, the problem of color reproduction errors is raised during the transition period.
On the other hand, if the color reproducing regions are different among different broadcasting systems, as indicated by a region 33 of a current television standard system, such as NTSC system, and a region 31 of the standard under the recommendations by CCIR REC XA/11, or if images having different image pickup characteristics, as indicated by a region 36 represented by the current television standard system by EBU (NTSC system) and the region 31 of the standard under the recommendations by CCIR REC XA/11, as shown in FIG. 5, are displayed simultaneously by the same television receiver, the reference white of the region 33 of the current television standard system, such as NTSC system, at point a, is different from the reference white of the region 32 of the standard under the recommendations by CCIR REC XA/11, at point b, so that color reproduction errors are produced.